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What is the ASME B31.3 hydrostatic test pressure formula?

Per ASME B31.3 Paragraph 345.4.2, the minimum hydrostatic test pressure is P_T = 1.5 × P × (S_T / S), where P is the internal design pressure, S_T is the allowable stress at the test temperature, and S is the allowable stress at the design temperature.

What is the minimum hold duration for a hydrostatic test under ASME B31.3?

ASME B31.3 does not mandate a fixed hold time in Paragraph 345. The test duration is governed by the owner’s engineering specification and applicable client standards; 10 to 30 minutes is common industry practice, with longer holds for large-bore or critical-service piping.

Can the test stress ratio S_T / S exceed 1?

Yes. When the allowable stress at the test temperature is higher than at design temperature, the ratio increases the test pressure proportionally. ASME B31.3 limits the ratio so that the combined longitudinal stress does not exceed 90% of the specified minimum yield strength at test temperature.

ASME B31.3 Hydrotest Pressure Calculator

Design Pressure, P (psig)

Allowable Stress at Test Temp, S_T (ksi)

Allowable Stress at Design Temp, S (ksi)

Minimum Hydrostatic Test Pressure

—psig

P_T = 1.5 × P × (S_T / S)

Code Compliance Note

Calculated per ASME B31.3 Paragraph 345.4.2. The minimum test pressure shall not be less than 1.5 times the design pressure adjusted for the stress ratio of test-to-design temperature. The pressure shall be verified at every point in the piping system.

Minimum Test Duration

ASME B31.3 does not mandate a fixed hold time. The duration is governed by the owner\u2019s specification and applicable client standards (e.g., Aramco SAES-W-011, ADNOC AGES). Industry practice commonly uses 10\u201330 minutes for standard piping, with longer holds for large-bore or critical-service lines.

The Hydrotest Formula

Per ASME B31.3 Paragraph 345.4.2, the minimum test pressure is P_T = 1.5 × P × (S_T / S), where P is the design pressure, S_T is the allowable stress at test temperature, and S is the allowable stress at design temperature. The 1.5 factor provides a safety margin above the design pressure. When the test is performed at ambient temperature and the design temperature is higher, S_T / S is typically greater than 1, increasing the test pressure proportionally.

How to Use This Calculator

Enter the design pressure (P) in psig — the maximum operating pressure of the system.

Enter the allowable stress at test temperature (S_T) in ksi — from ASME B31.3 Table A-1 at ambient temperature.

Enter the allowable stress at design temperature (S) in ksi — from Table A-1 at the design temperature.

The calculator outputs the minimum test pressure in psig. Round up to the nearest gauge increment.

Stress Ratio and Code Limits

When S_T is higher than S (common when testing at ambient but designing for elevated temperature), the ratio increases the test pressure. ASME B31.3 limits the test so that the combined longitudinal stress does not exceed 90% of the specified minimum yield strength (SMYS) at test temperature. If the calculated pressure would exceed this limit, the test pressure must be reduced. Always verify against the code and client specification.

Test Duration and Hold Time

ASME B31.3 does not mandate a fixed hold duration — it is governed by the owner's specification and applicable client standards. Aramco SAES-W-011 and ADNOC AGES typically require 10–30 minutes for standard piping, with longer holds for large-bore or critical-service lines. The test is visually inspected for leaks at all joints, flanges, and fittings during the hold period. Any leak requires depressurization, repair, and re-test.